A Simple Point (that makes a big difference over time)

Here at The Overpopulation Project we explore various aspects of the population-environment connection, some of which get quite complicated. In this blog we make a simple point, well worth remembering and sharing with colleagues and friends. We highlight the difference between a decreasing rate of global population growth, the amount of growth, and an end to growth. These distinctions about growth are regularly confounded in the media and in conversations about population.

by Philip Cafaro

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A few weeks ago, I was discussing the role ending global population growth could play in helping curb greenhouse gas emissions and limit global climate change. My conversation partner was an atmospheric scientist with a strong commitment to educating the public on climate matters. In the course of our discussion, he offered that the world had made “incredible progress in reducing population growth,” based on the sharp decrease in TFRs (total fertility rates) achieved by many countries around the world in recent decades.

His comments were a reminder that progress has been made and thus that progress can be made. This, of course, is good to keep in mind. He also got me thinking about the ambiguity in a statement like “progress in reducing population growth.”

It is true that as fertility rates have come down around the world, the rate of global population growth has slowed. Forty years ago, the world population was increasing at a little less than 2% per year. Today, that figure is closer to 1% annual growth (see Table 1). That looks like progress.


But note, the rate of growth is for a much larger human base. Forty years ago, the world was adding about 80 million people annually. Today, the world is adding—about 80 million people annually (82.6 million last year, according to one estimate). Thus, the amount of population growth has stayed about the same during this period (see Table 2). That doesn’t look like progress, but like continuation of an unacceptable status quo.

Furthermore, in a world where humanity is seeking safe use of biospheric resources (at least in declarations from the UN), any increase in the total number of people is going in the wrong direction. Remember that it is total numbers that drive humanity’s unsustainable demands on global ecosystems. As long as the global population is increasing, those demands will tend to keep increasing as well. Real progress toward sustainability demands not merely a decrease in the amount of population growth worldwide, but an end to such growth—hopefully followed by its reversal. Until we reach an end to growth, we may speak of progress toward that end, but certainly not of sufficient progress.


Figure 1 below, borrowed from McDevitt 1999, graphs both total global population (black line) and the decadal increase in population numbers (bars) from 1750-2050. The figure reminds us that a decrease in the amount of population increase can still add up to substantial overall population increase. It should be noted that the projected decreases for the last three decades (2020-2050) now seem unlikely to happen, since they require a more rapid decrease in global fertility rates than appears to be occurring.

Figure 1. Total global population and decadal increases in global population, 1750-2050.  Actual data for 1750 through 1990 and projections beyond 1990. From McDevitt 1999.

Whether the trends projected in McDevitt 1999 would represent sufficient progress toward sustainability might be matter for debate. But assuming a continued downward trend in population increase after 2050, the end of global population growth would at least be in sight.

However, there is no reason for complacency. First, we have good evidence that humanity’s current population is unsustainable, in warming temperatures, acidifying oceans, disappearing wildlife and increasing arguments over allocating fresh water. Second, neither a smooth transition from increasing to decreasing amounts of population growth, nor its continuation, is guaranteed. Recently, a stall in the declining fertility rates in African countries and elsewhere has reversed the trend toward smaller annual increases in the global human population, as shown in comparison between McDevitt’s projected data and actual data for the past three decades (Figure 2).

Figure 2. Comparison between past projections and actual growth for the past three decades. (a) Total global population and decadal increases in global population, 1750-2050.  Actual data for 1750 through 1990 and projections beyond 1990. From McDevitt 1999. (b) Total global population and decadal increases in global population, 1990-2020. Data from United Nations, World Population Prospects 2017. Actual data for 1990 through 2015 and medium projection data for 2015-2020. Orange bar highlights the discrepancy between past projected decline and the actual current increase in decadal growth.

Future human population numbers are not set in stone. They will be a function of government policies and billions of individual decisions. And most recently we seem to be moving further away from the goal of population stabilization, as Jane O’Sullivan shows in a figure from her recent publication “Synergy between Population Policy, Climate Adaptation and Mitigation” (2017). Figure 3, borrowed with her kind permission, shows that as international aid for family planning has declined in recent decades, the declining population increases expected by UN demographers have failed to materialize. Instead, humanity seems stuck on a “constant fertility” path set to deliver increasing additions to global human numbers.

Figure 3. Annual increase of global population, 1990–2010, and that projected under the UN’s medium fertility and constant fertility projections of 2013. Black circles give estimates of actual increase reported annually in the Population Reference Bureau’s “World Population Datasheets” (2011–2016). International aid spending on family planning is plotted against the right axis. From O’Sullivan, 2017.

Again, the evidence suggests that there is no room for complacency. We need to distinguish between rates of population increase, amounts of population increase, and an end to population increase—and work to achieve the latter. Ending population growth is a necessary part of achieving global environmental sustainability, and humanity is nowhere near doing so.


McDevitt, T. Knowledge-Based Population Projections: New Statistical Evidence and a Word on Making Projections under Real World Conditions. Poster presented at the Population Association of America meetings; New York; March 1999.

O’Sullivan JN. Synergy between Population Policy, Climate Adaptation and Mitigation. In: Hossain M, Sarker T, Hales R, eds. Pathways to a Sustainable Economy. Cham, Switzerland: Springer International; 2017:103-127.

United Nations Population Division. World Population Prospects. 2017.


Do you want to learn more about the solutions for overpopulation and actions towards sustainability? What actions we need to take on individual, community, national and global level? Check out the Overpopulation Project’s list of solutions!

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7 thoughts on “A Simple Point (that makes a big difference over time)

  1. Recently I read a heartfelt article on ‘Unherd’ extolling the wilding movement here in the UK: https://unherd.com/2019/05/why-wilding-should-make-our-hearts-sing/

    How this will work in our increasingly crowded country remains to be seen; the sentiments are laudable, but do not take any serious account of rising population pressure, with its inevitable demands on land,water, infrastructure , housing and transport.

    I keep reading about the currently fashionable dictum; ‘more people means more solutions’.

    Humanity is apparently unable to escape from the oxymoronic assumption that climate change, species loss,water shortages, mass extinctions and mass movements of people can all be solved without addressing the need to reduce our numbers.

    1. Yes, if you go to the excellent website for Rewilding Europe, you see that very often it is declining rural populations or declining agricultural demands that open up opportunities for rewilding. This is a theme in rewilding in the Coa Valley in Portugal, the Appennines in Central Italy, the Danube delta in Romania and the Oder delta on the German/Polish border, and elsewhere.

      Fewer people is good for wild nature, in many ways!

  2. People playing down the problems of overpopulation often refer to the first line in the first table (decrease of average global TFR). This article is an excellent overview of some other figures that matter. Thank you, Phil.

  3. Overpopulation is not in the main stream of news events. If we ever seek to make a dent to dramatically decrease our planet’s population, radical solutions must be addressed. Yet, so far even with organizations like OverPopulation.org with its dozens of member groups, nothing is rising to the top of main stream consciousness.

    Today, nothing short of a gigantic meteor strike will solve this problem.

    People with brains and money, think Bill Gates, Warren Buffett, Richard Branson, Elon Musk are basically gutless to advocate severe measures to stop overpopulation. They and many others can bring the dire issues of overpopulation to be addressed on the main stage of preserving life on our planet. Yet, we see precious little activity to do so.

    Since humans care so little to help our planet and the future of humanity, Mother Nature has already stepped in. She is creating her own version to quell population expansion by accelerating the decline of our oceans so aquatic food sources will deminish to the point of extinction. Oceans will rise overtaking coastal areas where billions now live, and in the process billions will die. Fertile fields will become deserts and hunger will starve billions. Fresh water reserves will dwindle and billions will die.

    New wars will be waged to access areas where crop growth and fresh water is still viable. Again, billions will die in these conflicts around the world. Ebola and other vicious diseases will consume billions.

    The sad part of Mother Nature’s handiwork will be severe and yet slow meaning death will not be quick, death will come in measured steps making humanity suffer for it’s recklessness.

    If anyone reading this has children then I pity you and especially your children who will see a new and very ugly world order.

    Our global time clock is nearing 2050 when the tipping point will be reach and it will be undoable.

    Tick tock.

  4. Worth noting that the much quoted UN projections have been revised upwards in each of 5 revisions since 2002. In 2002 the 2050 projection was 8.9 billion. In the 2017 revision the 2050 projection was 9.8 billion. Even the graphs here show falling rates of population growth in the projection period, but not in the actual numbers to date. More effort is going to be needed. Births need to be cut by 80 million a year. That’s a tall order given lack of funding for family planning, cultural barriers, pushback from pro-growth factions and religious lobbying against family planning and abortion. The good news is that fertility transitions have happened in 90 countries with TFR less than 2.1. It can be done. Bad news is that the toughest transitions due to culture and religion and lack of family planning services are yet to be accomplished.

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